Regulation of calcium carbonate polymorphs from recycled cement paste powder leachate and their impact on cement properties

The controlled preparation of calcium carbonate polymorphs from construction waste materials and their effects on cement performance remain significant challenges in sustainable construction material development. This work presents an innovative method for selective synthesis of calcite, aragonite and vaterite from recycled cement paste powder through ammonium chloride leaching followed by controlled carbonation using aqueous ammonia, magnesium hydroxide and glycine as crystallization modifiers. Material characterization revealed distinct morphological features: cubic calcite with specific surface area of 16.03 m2/g, needle-shaped aragonite at 17.78 m2/g, and spherical vaterite particles measuring 33.68 m2/g. Experimental results demonstrate that vaterite modification improves cement mortar flowability by 11.5 % and increases compressive strength by 31.2 % at 1 day and 7.3 % at 28 days, while calcite and aragonite incorporation reduces these properties by 6.4-13.9 %. Microstructural analysis indicates vaterite functions simultaneously as physical filler and chemical participant in hydration reactions, reducing porosity and promoting formation of hydration products, whereas calcite and aragonite primarily exhibit physical filling effects. These findings provide new understanding of structure-property relationships in calcium carbonate-modified cementitious systems and establish an effective approach for construction waste recycling that enhances material performance while reducing environmental impact. The developed polymorph control technology enables tailored material design for specific application requirements, representing an important advancement in sustainable cement technology.